Liang Jian, Scoles Giacinto
Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA.
Langmuir. 2007 May 22;23(11):6142-7. doi: 10.1021/la063385t. Epub 2007 Apr 25.
Nanografting, an atomic force microscopy (AFM) based nanolithography technique, is becoming a popular method for patterning self-assembled monolayers (SAMs). In this technique, a nanoscale patch of a thiol-on-gold SAM is exchanged with a different thiol by the action of an AFM tip operated in contact mode at high load. The results are then imaged in topographic or lateral force microscopy again at low values of the load. One of the problems of contact mode nanografting is that monolayers of large molecules such as proteins are likely to be deformed, damaged, or even removed from the surface by contact mode imaging even when small loads are used. Furthermore, we need to note that the stiffness of the cantilevers used in contact mode is different than that of the cantilevers used in tapping mode and that tip changing in the course of an experiment can be quite inconvenient. Here, we show that a monolayer on a gold substrate can be nanografted using tapping mode AFM (also referred to as amplitude modulation AFM) rather than the commonly used contact mode. While the grafting parameters are somewhat trickier to choose, the results demonstrate that nanografting in tapping mode can make patches of the same quality as those made by contact mode, therefore allowing for gentle imaging of the grafted molecules and the whole SAM without changing the microscope tip.
纳米嫁接是一种基于原子力显微镜（AFM）的纳米光刻技术，正成为一种用于对自组装单分子层（SAMs）进行图案化的流行方法。在该技术中，通过在高负载下以接触模式操作的AFM针尖的作用，金表面硫醇自组装单分子层的纳米级斑块会与不同的硫醇进行交换。然后在低负载值下再次通过形貌或侧向力显微镜对结果进行成像。接触模式纳米嫁接的问题之一是，即使使用小负载，蛋白质等大分子的单分子层也可能在接触模式成像过程中发生变形、受损甚至从表面脱落。此外，我们需要注意的是，接触模式中使用的悬臂梁的刚度与轻敲模式中使用的悬臂梁的刚度不同，并且在实验过程中更换针尖可能会非常不方便。在此，我们表明可以使用轻敲模式原子力显微镜（也称为振幅调制原子力显微镜）而非常用的接触模式对金基底上的单分子层进行纳米嫁接。虽然嫁接参数的选择稍微复杂一些，但结果表明轻敲模式下的纳米嫁接能够制作出与接触模式下质量相同的斑块，因此无需更换显微镜针尖就能对嫁接分子和整个自组装单分子层进行轻柔成像。
